1. Field of the Invention
The present invention relates to an ion beam assisted method of producing a diamond like carbon (DLC) coating on the surface of a material. More particularly, the invention relates to an ion beam assisted method using a fullerene precursor to produce a DLC coating, wherein the chemical composition of the ion beam and precursor are selectively chosen to determine the physical properties of the DLC coating.
2. Description of the Prior Art
DLC coatings have been used in the prior art to provide a material with a hard outer coating. By minimizing the hydrogen content of a DLC coating, the hardness of the coating can be increased. The presence of hydrogen in a DLC coating can impair the infrared transmission capabilities of the DLC coating because of the absorption of energy in existing carbon-hydrogen (C-H) vibrations. Thus, it is desirable to minimize the content of hydrogen in a DLC coating.
Prior art methods for applying a DLC coating have employed vaporizable precursors such as low vapor pressure hydrocarbons, organo-metallic compounds, and siloxanes. In these prior art methods, energetic ions, typically with energies in the range of 5-100 KeV, are used to bombard a condensed film of the precursor in order to rupture C-H bonds, thereby releasing hydrogen from the precursor into the ambient environment. This ion bombardment results in a film consisting mainly of carbon with an atomic hydrogen content of approximately 10-15%. The precursor will also contain elements which were present before the ionic bombardment, as well as atomic species present in the ions used for bombardment.
It is desirable to use carbon in the form of graphite as a precursor in ion beam assisted methods to produce a DLC coating; however, the deposition of carbon by thermal evaporation requires a large dissipation of energy, either in a carbon arc or in the form of a powerful electron beam. Such sources of thermally evaporated carbon are likely to heat the material or workpiece to be coated, possibly altering or impairing its physical properties. Thus, prior art methods have not proven effective in allowing the use of carbon in the form of graphite for use in an ion beam assisted method of producing a DLC coating.
Prior art methods have used pulse laser deposition of carbon in order to deposit the carbon in a vacuum. This method is inefficient and costly. Its costs make it economically unattractive for large scale industrial application.
Another method of applying carbon is through dual ion beam sputtering. Because of carbon's low atomic number, dual ion beam sputtering is an inefficient method of depositing carbon. Prior art methods of depositing a DLC coating are expensive and inefficient.